zabbix_agentd fails to start with error
"cannot attach shared memory for disk statistics collector:
[22] Invalid argument"
Note this doesn't look like the "cannot allocate shared mem" issue in the docs
(here we have "cannot attach shared memory", not "allocate")

Since it is unlikely that you have a similar machine (Raspberry Pi is armv6), I will be happy to follow instructions for debugging.

Agent works fine with same OS (except kernel rev) on Trimslice with Tegra arm7l architecture wit hFloating Point hardware support.

working system:-

[root@trimslice ~]# sysctl -a | grep shm
kernel.shmmax = 33554432
kernel.shmall = 2097152
kernel.shmmni = 4096

failing system:

[drew@alarm-1 ~]$ sysctl -a |grep shm
kernel.shmmax = 33554432
kernel.shmall = 2097152
kernel.shmmni = 4096
kernel.shm_rmid_forced = 0

working:
Linux trimslice 2.6.38-6-ARCH #1 SMP PREEMPT Tue Jan 3 04:23:49 UTC 2012 armv7l

failing:
Linux alarm-0 3.1.10-12-ARCH #1 PREEMPT Tue Jul 17 04:51:16 UTC 2012 armv5tel GNU/Linux

Since it appears to error on disk stats collector, the disk devices do seem to differ:

[root@trimslice ~]# cat /proc/diskstats
1 0 ram0 0 0 0 0 0 0 0 0 0 0 0
1 1 ram1 0 0 0 0 0 0 0 0 0 0 0
<snip>
1 14 ram14 0 0 0 0 0 0 0 0 0 0 0
1 15 ram15 0 0 0 0 0 0 0 0 0 0 0
7 0 loop0 0 0 0 0 0 0 0 0 0 0 0
7 1 loop1 0 0 0 0 0 0 0 0 0 0 0
<snip>
7 6 loop6 0 0 0 0 0 0 0 0 0 0 0
7 7 loop7 0 0 0 0 0 0 0 0 0 0 0
179 0 mmcblk0 5623 56 159676 21870 11125 1468 110328 6899170 0 3451170 6921010
179 1 mmcblk0p1 5548 56 159076 21500 11125 1468 110328 6899170 0 3451120 6920640

mmcblk0p1 is the partition containing the root fs

[root@alarm-0 zabbix_agent]# cat /proc/diskstats
1 0 ram0 0 0 0 0 0 0 0 0 0 0 0
1 1 ram1 0 0 0 0 0 0 0 0 0 0 0
<snip>
1 14 ram14 0 0 0 0 0 0 0 0 0 0 0
1 15 ram15 0 0 0 0 0 0 0 0 0 0 0
7 0 loop0 0 0 0 0 0 0 0 0 0 0 0
7 1 loop1 0 0 0 0 0 0 0 0 0 0 0
<snip>
7 6 loop6 0 0 0 0 0 0 0 0 0 0 0
7 7 loop7 0 0 0 0 0 0 0 0 0 0 0
31 0 mtdblock0 0 0 0 0 0 0 0 0 0 0 0
31 1 mtdblock1 0 0 0 0 0 0 0 0 0 0 0
31 2 mtdblock2 0 0 0 0 0 0 0 0 0 0 0
8 0 sda 6735 3137 187140 86830 138193 38202 2283488 62720800 0 706720 63017690
8 1 sda1 6660 3137 186540 86740 138193 38202 2283488 62720800 0 706710 63017600

sda1 is the partition holding the root fs, not sure what the mtdblock devices are but they're not on the "working" Trimslice.
Could it be that the error: "cannot attach shared memory for disk statistics collector: [22] Invalid argument" is due to the zabbix agent failing to understand the device 31 mtdblock devices?

Running zabbix_agentd with p works fine:

[root@alarm-0 zabbix_agent]# zabbix_agentd -p
agent.hostname [s|alarm-0]
agent.ping [u|1]
agent.version [s|2.0.2]
system.localtime [u|1345423957]
system.run [m|ZBX_NOTSUPPORTED]
web.page.get [t|EOF]
web.page.perf [d|0.000000]
web.page.regexp [s|EOF]
vfs.file.size [u|491]
vfs.file.time [u|1343061420]
vfs.file.exists [u|1]
vfs.file.contents [t|root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/bin/false
daemon:x:2:2:daemon:/sbin:/bin/false
mail:x:8:12:mail:/var/spool/mail:/bin/false
ftp:x:14:11:ftp:/srv/ftp:/bin/false
http:x:33:33:http:/srv/http:/bin/false
nobody:x:99:99:nobody:/:/bin/false
dbus:x:81:81:System message bus:/:/bin/false
ntp:x:87:87:Network Time Protocol:/var/empty:/bin/false
puppet:x:52:52:Puppet:/var/lib/puppet:/sbin/nologin
drew:x:1000:1000::/home/drew:/bin/bash
zabbix:x:1001:1001::/var/lib/zabbix:/bin/bash]
vfs.file.regexp [s|root:x:0:0:root:/root:/bin/bash]
vfs.file.regmatch [u|1]
vfs.file.md5sum [s|52316bf02f91c5d2515d3d5a363cd259]
vfs.file.cksum [u|3448930709]
net.dns [u|1]
net.dns.record [t|zabbix.com SOA ns1.yourhostingaccount.com admin.yourhostingaccount.com 2012081367 10800 3600 604800 3600]
net.tcp.dns [u|1]
net.tcp.dns.query [t|zabbix.com SOA ns1.yourhostingaccount.com admin.yourhostingaccount.com 2012081367 10800 3600 604800 3600]
net.tcp.port [u|0]
system.hostname [t|alarm-0]
system.uname [t|Linux alarm-0 3.1.10-12-ARCH #1 PREEMPT Tue Jul 17 04:51:16 UTC 2012 armv5tel GNU/Linux]
system.users.num [u|1]
log [m|ZBX_NOTSUPPORTED]
logrt [m|ZBX_NOTSUPPORTED]
eventlog [m|ZBX_NOTSUPPORTED]
kernel.maxfiles [u|51106]
kernel.maxproc [u|32768]
vfs.fs.size [u|14013427712]
vfs.fs.inode [u|928421]
vfs.fs.discovery [s|{
"data":[
{
"

":"\/",
"

":"devtmpfs"},
{
"

":"\/sys",
"

":"tmpfs"},
{
"

":"\/dev\/shm",
"

":"tmpfs"},
{
"

":"\/proc\/sys\/fs\/binfmt_misc",
"

":"binfmt_misc"}]}]
vfs.dev.read [u|6735]
vfs.dev.write [u|2283880]
net.tcp.listen [u|0]
net.udp.listen [u|0]
net.if.in [u|150284949]
net.if.out [u|150284949]
net.if.total [u|300569898]
net.if.collisions [u|0]
net.if.discovery [s|{
"data":[
{
"

":"eth0"},
{
"

":"eth1"}]}]
vm.memory.size [u|523644928]
proc.num [u|0]
proc.mem [u|0]
system.cpu.switches [u|39578123]
system.cpu.intr [u|51163897]
system.cpu.util [m|ZBX_NOTSUPPORTED]
system.cpu.load [d|0.000000]
system.cpu.num [u|1]
system.hw.chassis [m|ZBX_NOTSUPPORTED]
system.hw.cpu [m|ZBX_NOTSUPPORTED]
system.hw.devices [m|ZBX_NOTSUPPORTED]
system.hw.macaddr [s|[eth0] f0:ad:4e:ff:14:61]
system.sw.arch [s|armv5tel]
system.sw.os [s|Linux version 3.1.10-12-ARCH (nobody@platinum) (gcc version 4.7.1 (GCC) ) #1 PREEMPT Tue Jul 17 04:51:16 UTC 2012]
system.sw.packages [t|[pacman] acl 2.2.51-2, attr 2.4.46-2, autoconf 2.69-1, automake 1.12.2-1, bash 4.2.037-1, binutils 2.22-8, bison 2.6.2-1, bzip2 1.0.6-4, ca-certificates 20120623-1, cloog 0.17.0-2, coreutils 8.17-3, cracklib 2.8.18-2, cronie 1.4.8-3, cryptsetup 1.5.0-1, curl 7.26.0-1, dash 0.5.7-2, db 5.3.21-1, dbus-core 1.6.4-1, device-mapper 2.02.97-1, dhcpcd 5.5.6-1, diffutils 3.2-1.1, dirmngr 1.1.0-4, distcc 3.1-7, dnssec-anchors 20120422-1, e2fsprogs 1.42.4-1, eventlog 0.2.12-3, expat 2.1.0-1, facter 1.6.8-1, fakeroot 1.18.4-1, file 5.11-1.2, filesystem 2012.7-1, findutils 4.4.2-4, flex 2.5.37-1, fuse 2.9.1-1, gawk 4.0.1-1, gcc 4.7.1-5, gcc-libs 4.7.1-5, gdbm 1.10-1, gettext 0.18.1.1-4, git 1.7.11.4-1, glib2 2.32.4-1, glibc 2.16.0-1, gmp 5.0.5-1, gnupg 2.0.19-2, gpgme 1.3.1-4, gpm 1.20.6-10, grep 2.13-2, groff 1.21-2, gzip 1.5-1, heirloom-mailx 12.5-3, hwids 20120730-1, iana-etc 2.30-3, inetutils 1.9.1-2, initscripts 2012.07.5-1, iproute2 3.4.0-2, iputils 20101006-4, isl 0.10-1, jfsutils 1.1.15-3, kbd 1.15.3-3, keyutils 1.5.5-3, kmod 9-2, krb5 1.10.3-1, ldns 1.6.13-1, less 444-3, libarchive 3.0.4-1, libassuan 2.0.3-1, libcap 2.22-3, libedit 20120311_3.0-1, libfetch 2.33-1, libffi 3.0.11-1, libgcrypt 1.5.0-3, libgpg-error 1.10-2, libgssglue 0.3-1, libidn 1.25-1, libksba 1.2.0-1, libldap 2.4.32-1, libltdl 2.4.2-6, libmpc 0.9-2, libnl 3.2.11-1, libpcap 1.3.0-1, libpipeline 1.2.1-1, libsasl 2.1.23-9, libsigsegv 2.10-1, libssh2 1.4.2-1, libsystemd 188-2, libtirpc 0.2.2-2, libtool 2.4.2-6, libusb-compat 0.1.4-2, libusbx 1.0.12-2, libyaml 0.1.4-2, licenses 2.9-1, linux 3.1.10-12, linux-api-headers 3.4.6-1, linux-firmware 20120625-1, linux-headers 3.1.10-12, logrotate 3.8.2-1, lvm2 2.02.97-1, m4 1.4.16-2.1, make 3.82-4, man-db 2.6.2-1, man-pages 3.41-1, mdadm 3.2.5-2, mkinitcpio 0.10-1, mkinitcpio-busybox 1.20.1-1, mpfr 3.1.1-1, nano 2.2.6-2, ncurses 5.9-3, net-tools 1.60.20110819cvs-3, ntfs-3g 2012.1.15-3, openntpd 3.9p1-15, openssh 6.0p1-3, openssl 1.0.1.c-1, package-query 1.0.1-1, pacman 4.0.3-2, pacman-mirrorlist 20120608-1, pam 1.1.5-4, pambase 20120701-1, patch 2.6.1-3, pciutils 3.1.10-1, pcmciautils 017-1, pcre 8.31-1, perl 5.16.1-1, perl-error 0.17018-1, pinentry 0.8.1-4, pkg-config 0.27-1, popt 1.16-5, ppl 1.0-1, ppp 2.4.5-3, procps-ng 3.3.3-3, psmisc 22.19-1, pth 2.0.7-4, puppet 2.7.17-1, readline 6.2.004-1, reiserfsprogs 3.6.21-4, rsync 3.0.9-3, ruby 1.9.3_p194-2, ruby-shadow 1.4.9-4, run-parts 4.3.2-1, screen 4.0.3-13, sed 4.2.1-4, shadow 4.1.5.1-1, strace 4.7-1, sudo 1.8.5.p2-1, sysfsutils 2.1.0-8, syslog-ng 3.3.5-2, systemd-tools 188-2, sysvinit 2.88-6, tar 1.26-2, tcp_wrappers 7.6-15, texinfo 4.13a-7, tzdata 2012e-1, usbutils 006-1, util-linux 2.21.2-5, vi 1:050325-2, vim 7.3.600-1, vim-runtime 7.3.600-1, wget 1.14-1, which 2.20-5, wpa_supplicant 1.0-1, xfsprogs 3.1.8-2, xz 5.0.4-1, yajl 2.0.4-1, yaourt 1.1-1, zabbix-agent 2.0.2-1, zlib 1.2.7-1]
system.swap.size [u|0]
system.swap.in [u|0]
system.swap.out [u|0]
system.uptime [u|2377393]
system.boottime [u|1343046566]
sensor [m|ZBX_NOTSUPPORTED]
net.tcp.service [u|1]
net.tcp.service.perf [d|0.044363]

zabbix_agentd -t <key> for the disk device stats gives mixed results but note the segfaults for the abbreviated Sectors and Operations parameters.

[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,sectors]
vfs.dev.read[,sectors] [u|373680]
[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,operations]
vfs.dev.read[,operations] [u|13395]
[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,bytes]
vfs.dev.read[,bytes] [m|ZBX_NOTSUPPORTED]
[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,sps]
Segmentation fault
[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,ops]
Segmentation fault
[root@alarm-0 zabbix_agent]# zabbix_agentd -t vfs.dev.read[,bps]
vfs.dev.read[,bps] [m|ZBX_NOTSUPPORTED]